1. Field of the Invention
The invention relates to a method and a device for the precision machining of crankshafts or camshafts to final size tolerances Rz<10 μm, preferably ≦5 μm, and concentricity tolerances≦30 μm, preferably ≦6 μm. The crankshafts or camshafts have been machined by a cutting operation and at least partly subjected to hardening.
2. Description of Related Art
In the machining methods known according to the prior art, the crankshafts normally pass through a plurality of machining stages. First of all, the cast or forged shafts are subjected to a cutting operation, such as turn broaching, turn-turn broaching, internal rotary milling and external milling, especially at high milling speeds wherein the allowance provided from the casting or forging point of view is removed down to a residual value within the millimeter range.
In order to increase the abrasion resistance of the crankshaft, the shaft is at least partly hardened according to a further step, for example by induction hardening, in order to achieve the desired material structure or microstructure. During the hardening, a distortion and a slight dimensional change of the crankshaft or of the camshaft cannot be ruled out, which has to be compensated for in a subsequent machining step.
The crankshafts are normally ground in a third machining step, for example using a grinding wheel, the axis of rotation of which moves parallel to the axis of rotation of the rotating crankshaft or camshaft. The grinding is mostly carried out with the addition of cooling lubricants in order to avoid excessive heating of the crankshaft during the subsequent grinding operation. Apart from the fact that the disposal of the resulting grinding sludge, which contains both the ground-off shaft particles and the torn-out abrasive grains of the grinding wheel, is costly, since grinding sludge has to be handled as special waste, considerable heating of the workpiece cannot be completely ruled out, nor can unfavorable effects on the workpiece surface, which produce an undesirable surface structure within the microscopic range as a result of the high machining pressures during the grinding.